Many portable audio devices have numerous functions. Each of these functions may have one or more digital audio bit streams associated with it, which may each have different sampling frequencies and which require conversion to an analog format for playback. Problems, however, arise with mixing and power consumption because most codecs used for such applications consume a great deal of power to provide asynchronous audio playback.
Some examples of conventional circuits are: European Patent No. 0673018A2; U.S. Pat. No. 7,330,812; U.S. Pat. No. 7,487,193; U.S. Patent Pre-Grant Publ. No. 2004/0068399; and U.S. Patent Pre-Grant Publ. No. 2005/0018862.